Found on the Twitter feed of Salvatore Sanfilippo (@antirez):
The document by Dan Luu is “What’s New in CPUs Since the 80s and How Does It Affect Programmers?”. It is focused for application developers, not firmware developers. Regardless, it is a good overview of changes in CPU technologies, covering caching, concurrency, different kinds of memory, GPUs, and a bit on porting to non-x86 systems, and about a dozen other topics. Worth reading!
http://danluu.com/new-cpu-features/
For a more detailed description of some of the other Intel platform changes, also read this book:
Firmware Security 